DIESEL COOLING SYSTEM SERVICE
BY TERRY ECKERT
It is that time of year when the cooling system might let you down. The diesel motor is more demanding on the cooling system, especially in the warmer weather.
Nowadays with the great engineering improvements that have taken place, you hear about fewer problems with gasoline motors overheating or blowing head gaskets. These problems, however, seem to be increasing with diesel motors, especially in the rigs we use in the emergency service. A significant percentage of today`s breakdowns are related to cooling system problems. We need to ask ourselves the following questions:
Why are we experiencing this problem?
Is this a maintenance problem?
Is it a usage problem over which we have no control?
Is it a lack of education on how to properly service the cooling system?
Is it a flaw in the engine or manufacturer`s design?
Were the vehicle`s specifications properly written?
Is it a driver-operator problem?
As you can see, any number of factors might cause cooling system problems. You will find that in most cases more that one of the above mentioned items are the culprits.
Electronic fuel injection, larger turbo chargers, and air charge coolers are worth mentioning here. These items have given us the horsepower and torque needed to push and pump our growing apparatus demands, but these changes have resulted in motor cooling system errors and less motor protection. These result in the growing liner and motor failure we have noticed over the past several years.
BASIC DESIGN
Let us begin with basic design and work our way up.
The manufacture of the vehicle. On fire apparatus, the commercial chassis has a history of fewer problems than the custom-built fire truck. There could be a number of reasons for this. One that comes to mind is that the commercial builders build many more trucks and have the experience and engineering capabilities behind them. The assembly line (where everything is put together in the same manner) is an advantage. Over-the-road trucks are designed not to overheat while in city traffic, pulling long grades, or working in the heat of Mexico. These are extremes that your apparatus hopefully will not see.
The custom builder has all kinds of obstacles to overcome. Have you ever seen two fire chiefs agree on building trucks that are identical? That is the reason they spend the big bucks to build what they need and want. Of course, they will need different load requirements that will need different horsepower that produces heat that will have to be dissipated somehow. Oh, by the way, the chiefs are going out for bid on this project, so the builder cannot install the biggest, fanciest, and most expensive coolant system he can find. The builder will install the coolant system he figures will do the job. Unless the chief specs something different, the builder has to rely on charts, figures, and engineers to put in the apparatus the most economical system that will do the job. After all, he needs to be able to compete in the bidding war. The truck will operate just fine under the parameters of regular use (just as described in NFPA 1901, Automotive Fire Apparatus, 1996); but as the vehicle ages, equipment is added, electrical loads are added, and preventive maintenances (PMs) are missed, overheating will more than likely become a problem.
CONSIDERATIONS WHEN SPECIFYING A COOLING SYSTEM
When your specification committee discusses a cooling system for a new piece of apparatus, here is a list of things to consider:
Use the NFPA (current edition) as a minimum standard.
Install a radiator that is rated 150 percent to 200 percent oversized.
Install an oversized transmission cooling system.
Install coolant filter(s). Cooling systems are reported to have three times the breakdowns without coolant filters.
Install a temperature-operated fan clutch.
Air-conditioning systems should not have the condenser in front of the radiator. The condenser(s) should be on the roof or under the vehicle with the condenser cooling fans.
The radiator must have proper air flow with no restrictions and should include fan shrouds and shields to prevent heated air from recirculating around the radiator and passing back through.
The air charge cooler should not restrict or preheat airflow to the radiator. The cooler should be mounted parallel to the radiator.
Spec the vehicle to operate under a higher ambient temperature than is normal for your area. When writing your specs, include working conditions with a timeframe, such as “this vehicle will operate at normal operating temperature without overheating for a minimum of six (6) hours at +1157F.”
Order the option that has a tilt cab, even if it has an aerial device. It is not fun or cheap to remove a radiator from a non-tilt cab. If radiator overhaul is required, it`s no fun to have to cut a hole in the roof to have it removed. Even if you should be able to weasel the radiator out, you will be a believer in the tilt-cab theory. Spend the small amount of extra money on a tilt cab–the “pay me now or pay me later” theory applies here.
Specify a level sight glass and a remote coolant reservoir tank. A remote tank lets you add coolant without breaking into the pressurized system–a definite safety item. You might also want the sight glass and fill tank accessible without having to tilt the cab.
Specify silicone for all coolant hoses. Using stainless-steel, constant torque hose clamps is also a good idea. These hose clamps are designed to react to temperature changes and maintain constant pressure on the coolant hoses. This will reduce cold water leaks that cause coolant dilution.
Just in case the driver-operator gets sidetracked, install overheat warning buzzers and lights that operate on both the panel and dash. And whatever you do, don`t forget the low coolant warning light installed on the dash.
I cannot stress the importance of starting with the correct apparatus specification and construction. Engine builders today install automatic shutdowns into the electronic control modules (ECMs) but not on fire trucks. Fire apparatus is unique and has to perform in life-and-death situations. No automatic shutdowns are allowed. A failing cooling system will not shut down any automatic shutdown systems on the fire apparatus, so the only thing that will shut you down is the death of the motor.
Diesel fire apparatus have a motor designed to operate at 1807F. If the fire apparatus is designed properly, this motor should never run much above 1807F. The NFPA standards require that fire apparatus perform at full pump capacity with all accessories operating (including the air-conditioning and all emergency lights); the engine cooler off; and all engine hoods, covers, and doors closed, without overheating.
Remember, the key is that the normal motor operating temperature is 1807F. The motor (and all its components), the oil, and diesel fuel are all designed to run at 1807F. This is where the horsepower curve is rated, where torque is measured, and where the least bearing and piston wear occurs. It is also the world in which a diesel motor wants and needs to live.
Because of its design, a diesel motor will also lose power operating with an ambient (outside) air temperature of 907F or higher. At this temperature, the diesel motor has to work even harder to perform the same duty, and the demands on the cooling system are even greater.
Your specifications committee must consider all these things. Again, do not assume that the builder will do it for you.
ADDITIONAL MAINTENANCE ITEMS
Let`s take a look at other coolant maintenance items.
Visual coolant check. Visually inspect the coolant for any sign of oil. Small amounts of oil in the coolant will cause overheating. (Oil in the coolant might also indicate a defective transmission or oil cooler.) If there is any suspicion of oil in the coolant, take a sample and send it in for an analysis. Most dealerships can do the analysis.
Radiator. Visually check the radiator. Make sure the coolant sight glass is in good shape and the coolant can be easily seen. Look for obstructions to the airflow. Fins can get clogged with dirt, leaves, pine needles, oil, and grease. Clean the fins by soaking them in a cleaning solution and then rinsing with a garden hose. Look for fin deterioration. Fins have to be solid to transfer heat. If the fins are soft or disintegrate to the touch of a finger, replace the core. Fins are deteriorated by chemicals such as salt and seawater. Look for signs of leakage along seams, inlet and outlet fittings, and tubes. Inspect the tanks, tubes, header seams, and brackets to be sure they are straight and square. If any area of the radiator is bent, bowed, or bulging, it indicates prior extreme pressures or fatigue; repair or replace the radiator immediately. Use a heat sensor gun to check for internal clogging of the radiator; this is the same gun used to check for heat behind the walls. The part of the radiator that is clogged or restricted will be cooler than the rest of the radiator. If you think you have found a problem, have a radiator specialist check it out.
Hoses and clamps. Check for leakage or seepage, cuts, and rubbing. Check for flexibility. The hoses need to be flexible enough for motor vibration. Replace the hoses that are too stiff or too soft. Hoses that are too soft may indicate oil in the coolant. Replace hoses with silicone hoses. Replace clamps with stainless-steel, constant torque hose clamps. Check all clamps for tightness–rusty clamps may break.
Pressure-test coolant system. With today`s silicone hoses, cold leakage problems do exist. Invest in a cooling system pressure test tool with the truck adapters you need. The pressure test is usually the only way to find that cold leak problem. If a problem is found, the price of the tester can be offset by what it would cost to replace the coolant and SCA, let alone repair the motor. Make sure the coolant system holds pressure. Make sure to test the system at the manufacturer`s recommended operating pressure. Also, test the radiator cap at the same pressure. Visually check the cap for gaskets and vacuum relief valve and spring.
Coolant fan. Clean all oil, grease, and dirt from the fan blades so they will move the air in the right direction. Check to make sure that the fan clutch (if equipped) engages when the cooling system attains operation temperature. Some fan clutches have an oil sump; if so, fill it with the correct oil.
Fan shroud. Check for mounting and damage of the shroud and shields. Make sure that the air cannot recirculate around the shroud and back into the radiator. If the plastic fan shroud is cracked, replace it.
Heat shields. Remove the pump heat shields, if so equipped, that trap hot air from the muffler.
Thermostat(s). Check the thermostat(s) by using a heat sensor gun or temperature probe. Check the thermostat housing(s) outlet to see at what temperature the thermostat opens.
Heater control valves. Now is a good time to check the valves that open and close the coolant flow through the heater hoses. Stuck or open valve(s) will cause cab heaters to keep working, which will lead to a hotter motor, an overworked air-conditioning unit, and sweaty and upset firefighters.
Air-conditioning: Conduct annual basic refrigerant service. Check all the belts. Clean fins in the evaporators and condensers. Check and clean the condenser fans. A properly serviced air-conditioning system will run with lower compressor head pressure, which saves horsepower and heat.
DRIVER EDUCATION
Let us not forget that driver-operator education is an important part of the cooling maintenance program. The driver-operator must be able to recognize an overheating motor, know the department`s SOPs for possible emergency shutdowns on the fireground, and know the procedures for cooling down the motor. Drivers-operators must know the proper way of operating the auxiliary (heat exchanger) cooler located on the pump panel; how to locate and operate the emergency radiator fill, if so equipped; and how to fill the coolant system and which coolant to put in it.
Training on warm weather operations should be an annual event; all department procedures should be reviewed.
Coolant systems would operate just fine if this were a perfect world. But additive depletion, the operating condition of the engine, extreme environmental conditions, coolant loss and the resulting coolant replacement, and overlooked scheduled maintenance are some of the factors that can turn an otherwise careful coolant maintenance program into an ineffective one.
There have to be some checks and measures, such as a mandatory pre-hot weather coolant check, radiator fin and fan cleaning, coolant analysis, and a thermostat opening temperature check. Schedule a mandatory coolant change every two years.
Of course, one of the great sayings is “Nobody notices what I do until I don`t do it.” Well, if you don`t have coolant system maintenance on your To Do list, I will guarantee you that someone will notice when that coolant system blows! Sometimes, it`s nice not to be noticed. Next time, we`ll look at coolants. n
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Additional Items to Check
The following items might be added to your daily checks:
Check the coolant level by the sight glass or the level in the reservoir. Do not assume the last driver did it–the motor`s life and your next promotion could depend on that coolant check. Do not depend on the low coolant warnings installed on most new apparatus; they sometimes are too low in the radiator and do not always register. Remove the radiator only to fill it with coolant. Constant removal and reinstallation of the cap will wear out the gaskets, and the cap may not be reseated properly. Numerous apparatus have been declared dead because of a blown-off or lost radiator cap.
Check the front side of the radiator for debris such as leaves, pine needles, mud, and dirt. If air cannot get through the radiator fins, the coolant cannot cool the motor. Apparatus with center-mounted radiators suck the air from the road. This problem is commonly overlooked.
Check the fan belts (if so equipped). Check for tightness, wear, and cracks. If the belts squeal or make noise, replace them. Throw away that “belt dressing”; it does not work on today`s serpentine belts.
Check the hoses and the radiator for leaks. Visibly check the hoses and the radiator for signs of leakage. Coolant that is leaking or seeping over time will evaporate and leave a residue. Always look for puddles on the floor. If you find any unusual puddles–coolant, oil, or any other fluid–report them immediately to maintenance.
Check the engine coolant valve. Check to make sure it operates freely, and leave it in the closed position until it is needed.
Check both engine temperature gauges. There is one gauge on the panel and one gauge on the dashboard. Watch the gauges during start-up and warm-up, making sure that the motor warms up at the normal quickness to operating temperature (1807F) and then maintains that temperature. Compare the gauges against each other to make sure they are within 10 percent of each other.
Check motor oil and transmission oil levels. One of the jobs of the oil is to cool, so keep the oil levels to the full line.
TERRY ECKERT, a 16-year veteran of the fire service, is a firefighter and head of apparatus maintenance in the Darien-Woodridge (IL) Fire District and the chief engineer of the Westmont (IL) Fire Department. He has 25 years of experience as a vehicle technician. He is an ASE-certified master automobile technician and a master heavy truck technician and an EVT Level 3 master technician. He also has ASE certification in advanced level engine performance. Eckert is a member of numerous professional associations, including the National Association of Emergency Vehicle Technicians (NAEVT) and the Illinois Fire Apparatus Mechanics Association. He is a member of the EVT Certification Commission, where he serves on the Validation Committee and had chaired the E-3 section, and the NFPA Technical Committee on Emergency Vehicle Technician Professional Qualifications. He was the 1997 recipient of the NAEVT Certificate of Achievement Award.
